The permeability of a keratinizing squamous epithelium in culture.

Horseradish peroxidase or lanthanum was applied to the surface of keratinized oral epithelium growing in tissue culture and the extent of penetration of these substances examined with the electron microscope. Both tracer substances penetrated between the superficial keratinized squames of the tissue, the lanthanum reaching the basal cell layer and the peroxidase diffusing to within 3--8 cells of the basal layer. The permeability of the keratinized layer in this epithelium is in contrast to the situation in vivo where an intercellular barrier is found in the superficial layer. This difference might be related to the absence of membrane-coating granules from the tissue maintained in culture.